Oh, of course I believe you, and of course I believe Kirby said that because you said Kirby said that... But I'm also kinda sure that everyone else in the last 50 years has thought that he was made of rock, right down to Mallrats...

[Upon meeting Stan Lee] Brodie: The Thing! Is his dork made out of orange rock like the rest of his body? Stan Lee: I don't know. It's a superhero secret.